5,533 research outputs found
Extending the redshift distribution of submm galaxies: Identification of a z~4 submm galaxy
We present the identification of a bright submillimeter galaxy (SMG) in the
field of Abell 2218. The galaxy has a spectroscopic redshift of ~4, and is
currently the highest redshift SMG known. It is detected at all wavelengths
from optical to submm, including the Spitzer IRAC bands. We discuss the
properties of this galaxy, which is undergoing intense star formation at a
rate~600 Msun/yr. We also compare the properties to those of radio-preselected
submm-bright galaxies. The z~4 result extends the redshift distribution of
SMGs.Comment: 4 pages, 4 figures, uses asp2004.sty. To appear in the proceedings of
the conference "Infrared Diagnostics of Galaxy Evolution", Pasadena, CA,
14-16 November 2005, ed. R. Char
Physical properties and morphology of a newly identified compact z=4.04 lensed submillimeter galaxy in Abell 2218
We present the identification of a bright submm source, SMMJ163555.5+661300,
detected in the lensing cluster Abell2218, for which we have accurately
determined the position using observations from the Submillimeter Array (SMA).
The identified optical counterpart has a spectroscopic redshift of
z=4.044+-0.001 if we attribute the single emission line detected at
lambda=6140AA to Lyman-alpha. This redshift identification is in good agreement
with the optical/near-infrared photometric redshift as well as the submm flux
ratio S_450/S_850~1.6, the radio-submm flux ratio S_1.4/S_850 < 0.004, and the
24um to 850um flux ratio S_24/S_850 < 0.005. Correcting for the gravitational
lensing amplification of ~5.5, we find that the source has a far-infrared
luminosity of 1.3x10^12 Lsun, which implies a star formation rate of 230
Msun/yr. This makes it the lowest-luminosity SMG known at z>4 to date. Previous
CO(4-3) emission line obserations yielded a non-detection, for which we derived
an upper limit of the CO line luminosity of L'_CO = 0.3x10^10 K km/s/pc^2,
which is not inconsistent with the L'_CO - L_FIR relation for starburst
galaxies. The best fit model to the optical and near-infrared photometry give a
stellar population with an age of 1.4 Gyr and a stellar mass of 1.6x10^10 Msun.
The optical morphology is compact and in the source plane the galaxy has an
extent of ~6kpc x 3kpc with individual star forming knots of <500 pc in size.
J163556 is not resolved in the SMA data and we place a strict upper limit on
the size of the starburst region of 8kpc x 3kpc, which implies a lower limit on
the star formation rate surface density of 12 Msun/yr/kpc^2. The redshift of
J163556 extends the redshift distribution of faint, lensed SMGs, and we find no
evidence that these have a different redshift distribution than bright SMGs.Comment: Accepted for publication in ApJ. 11 pages, 7 figure
Computer program developed for flowsheet calculations and process data reduction
Computer program PACER-65, is used for flowsheet calculations and easily adapted to process data reduction. Each unit, vessel, meter, and processing operation in the overall flowsheet is represented by a separate subroutine, which the program calls in the order required to complete an overall flowsheet calculation
Economic, Neurobiological and Behavioral Perspectives on Building America's Future Workforce
A growing proportion of the U.S. workforce will have been raised in disadvantaged environments that are associated with relatively high proportions of individuals with diminished cognitive and social skills. A cross-disciplinary examination of research in economics, developmental psychology, and neurobiology reveals a striking convergence on a set of common principles that account for the potent effects of early environment on the capacity for human skill development. Central to these principles are the findings that early experiences have a uniquely powerful influence on the development of cognitive and social skills, as well as on brain architecture and neurochemistry; that both skill development and brain maturation are hierarchical processes in which higher level functions depend on, and build on, lower level functions; and that the capacity for change in the foundations of human skill development and neural circuitry is highest earlier in life and decreases over time. These findings lead to the conclusion that the most efficient strategy for strengthening the future workforce, both economically and neurobiologically, and for improving its quality of life is to invest in the environments of disadvantaged children during the early childhood years.
Energy efficient engine: Low-pressure turbine subsonic cascade component development and integration program
A subsonic cascade test program was conducted to provide technical data for optimizing the blade and vane airfoil designs for the Energy Efficient Engine Low-Pressure Turbine component. The program consisted of three parts. The first involved an evaluation of the low-chamber inlet guide vane. The second, was an evaluation of two candidate aerodynamic loading philosophies for the fourth blade root section. The third part consisted of an evaluation of three candidate airfoil geometries for the fourth blade mean section. The performance of each candidate airfoil was evaluated in a linear cascade configuration. The overall results of this study indicate that the aft-loaded airfoil designs resulted in lower losses which substantiated Pratt & Whitney Aircraft's design philosophy for the Energy Efficient Engine low-pressure turbine component
Preferential attachment of communities: the same principle, but a higher level
The graph of communities is a network emerging above the level of individual
nodes in the hierarchical organisation of a complex system. In this graph the
nodes correspond to communities (highly interconnected subgraphs, also called
modules or clusters), and the links refer to members shared by two communities.
Our analysis indicates that the development of this modular structure is driven
by preferential attachment, in complete analogy with the growth of the
underlying network of nodes. We study how the links between communities are
born in a growing co-authorship network, and introduce a simple model for the
dynamics of overlapping communities.Comment: 7 pages, 3 figure
Snell's Law for Shear Zone Refraction in Granular Materials
We present experiments on slow shear flow in a split-bottom linear shear
cell, filled with layered granular materials. Shearing through two different
materials separated by a flat material boundary is shown to give narrow shear
zones, which refract at the material boundary in accordance with Snell's law in
optics. The shear zone is the one that minimizes the dissipation rate upon
shearing, i.e.a manifestation of the principle of least dissipation. We have
prepared the materials as to form a granular lens. Shearing through the lens is
shown to give a very broad shear zone, which corresponds to fulfilling Snell's
law for a continuous range of paths through the cell.Comment: 4 pages, 5 figure
New CO detections of lensed submillimeter galaxies in A2218: Probing molecular gas in the LIRG regime at high redshift
Context: Submillimeter galaxies (SMGs) are distant, dusty galaxies undergoing
star formation at prodigious rates. Recently there has been major progress in
understanding the nature of the bright SMGs (i.e. S(850um)>5mJy). The samples
for the fainter SMGs are small and are currently in a phase of being built up
through identification studies. Aims: We study the molecular gas content in two
SMGs, SMMJ163555 and SMMJ163541, at z=1.034 and z=3.187 with unlensed submm
fluxes of 0.4mJy and 6.0mJy. Both SMGs are gravitationally lensed by the
foreground cluster A2218. Methods: IRAM Plateau de Bure Interferometry
observations at 3mm were obtained for the lines CO(2-1) for SMMJ163555 and
CO(3-2) for SMMJ163541. Additionally we obtained CO(4-3) for the candidate
z=4.048 SMMJ163556 with an unlensed submm flux of 2.7mJy. Results: CO(2-1) was
detected for SMMJ163555 at z=1.0313 with an integrated line intensity of
1.2+-0.2Jy km/s and a line width of 410+-120 km/s. From this a gas mass of
1.6x10^9 Msun is derived and a star formation efficiency of 440Lsun/Msun is
estimated. CO(3-2) was detected for SMMJ163541 at z=3.1824, possibly with a
second component at z=3.1883, with an integrated line intensity of 1.0+-0.1 Jy
km/s and a line width of 280+-50 km/s. From this a gas mass of 2.2x10^10 Msun
is derived and a star formation efficiency of 1000 Lsun/Msun is estimated. For
SMMJ163556 the CO(4-3) is undetected within the redshift range 4.035-4.082 down
to a sensitivity of 0.15 Jy km/s. Conclusions: Our CO line observations confirm
the optical redshifts for SMMJ163555 and SMMJ163541. The CO line luminosity
L'_CO for both galaxies is consistent with the L_FIR-L'_CO relation. SMMJ163555
has the lowest FIR luminosity of all SMGs with a known redshift and is one of
the few high redshift LIRGs whose properties can be estimated prior to ALMA.Comment: 7 pages, 4 figures. A&A in pres
Probing the submillimetre number counts at f(850 mu m) < 2mJy
We have conducted a submillimetre mapping survey of faint, gravitationally lensed sources, where we have targeted 12 galaxy clusters and additionally the New Technology Telescope (NTT) Deep Field. The total area surveyed is 71.5 arcmin^(2) in the image plane; correcting for gravitational lensing, the total area surveyed is 40 arcmin^(2) in the source plane for a typical source redshift z approximate to 2.5. In the deepest maps, an image plane depth of 1sigma rms similar to 0.8 mJy is reached. This survey is the largest survey to date to reach such depths. In total 59 sources were detected, including three multiply imaged sources. The gravitational lensing makes it possible to detect sources with flux density below the blank field confusion limit. The lensing-corrected fluxes range from 0.11 to 19 mJy. After correcting for multiplicity, there are 10 sources with fluxes 50 per cent) to the integrated background arises from sources with fluxes S-850 between 0.4 and 2.5 mJy, while the bright sources S-850 > 6 mJy contribute only 10 per cent
- …